The present invention relates to an electric spindle motor, in particular it relates to an electric spindle motor with an integrated magnetic bearing and hydrodynamic bearing for use in data storage devices such as hard disk drives, optical drives or other precision instruments.
Electric spindle motors are widely used in precision instruments such as hard disk drives, optical drives, magnetic-optical drives, printers or similar devices to meet high speed, high precision, low acoustic noise and low power consumption requirements of these applications. Conventional ball bearing spindle motors have been attempted for use in the above applications. Due to the drawbacks such as higher non-repeatable runout as well as higher acoustic noise caused by imperfect geometry on the inner race, outer race and the rolling elements, conventional ball bearing spindle motors are unlikely suitable for the next generation of precision instruments such as hard disk drives. Fluid film bearings have no direct surface contact during operation hence may be an alternative solution in replacement of the ball bearings for use in hard disk drives. One of the major difficulties for the application of fluid film bearing in hard disk drives is the liquid lubricant leakage which may degrades the performance of the fluid bearing. Lubricant leakage will also contaminate the surfaces of the disks leading to failures of the hard disk drive.
U.S. Pat. No. 5,283,491 to Jabbar et al and U.S. Pat. No. 5,760,509 to Chung et al disclose spindles with aerodynamic bearings which may have no risk of lubricant leakage. However, aerodynamic bearings have relatively lower load capacity and lower stiffness compared with the hydrodynamic bearings at similar range of geometric configuration. Furthermore, the rotor part and the stator part are electrically insulated hence there is no path for electrical discharge during operation of the spindle. This may result in possible damage of relevant part of the spindle such as the magneto-resistive (MR) head and cause failure of the hard disk drives. Aerodynamic bearings also have relative higher wear ratio, especially during the starting and stopping period of the spindle motor.
To overcome the above mention drawbacks in prior inventions, a hybrid bearing system, that is, an integration of hydrodynamic journal bearings and magnetic thrust bearings is provided by the present application. The present invention minimizes the friction between the bearing matting surfaces in a hydrodynamic thrust bearing therefore is power saving; fast starting and stopping with reduced contamination and cost-effective.
It is a first aspect of the present invention that an electric spindle motor disclosed has an improved radial load capacity and a reduced friction resistance.
It is a second aspect of the present invention that an integrated structure is disclosed for an electric spindle motor using a hydrodynamic journal bearing together with a magnetic bearing.
In accordance with the first and second aspects above, the electric spindle motor of the present invention comprises a stationary sub-assembly having a base and a first supporting means mounted on the base; a rotary sub-assembly having a rotating axis and a second supporting means for movably receiving the first supporting means; a hydrodynamic journal bearing interposed between the first and the second supporting means; and a magnetic bearing set positioned between the stationary sub-assembly and the rotary sub-assembly. The magnetic bearing set has at least one pair of electromagnets and at least one pair of thrust plates interactively associated with the at least one pair of electromagnets for controllably suspending the rotary sub-assembly from the stationary sub-assembly.
Preferably, the hydrodynamic journal bearing further comprises a first section, a second section and a gap therebetween for containing a lubricant.
Preferably, the electric spindle motor further comprises a sealing means for insulating the hydrodynamic journal bearing and discharging static electric charges from the rotary sub-assembly.
Preferably, the electric spindle motor further comprises at least one pair of permanent magnets respectively mounted on the at least on pair of thrust plates whereby providing a pre-load for keeping the rotary sub-assembly resting on the stationary sub-assembly.
Alternatively, the pair of electromagnets are offset from the pair of thrust plates along an axial direction of the rotating axis of the rotary sub-assembly.
Alternatively, the pair of electromagnets being offset from the pair of thrust plates along an redial direction of the rotating axis of the rotary sub-assembly.
Alternatively, the first supporting means comprises a shaft and the second supporting means comprises a sleeve.
Alternatively, the first supporting means comprises a sleeve and the second supporting means comprises a shaft.
The electric spindle motor having integrated hydrodynamic journal bearing and magnetic bearing of the present invention is capable of high speed and high accuracy running, providing increased radial load and stiffness, and reduces the friction resistance therefore improves the performance and power saving.